Method of and device for caching digital content data

ABSTRACT

The disclosure relates to a method of caching a part of digital content data from a content source ( 202 ), comprising the step of: acquiring the digital content data from the content source ( 202 ), wherein said part of the digital content data comprises interleaved segments ( 130; 131 ) of the acquired digital content data, and said interleaved segments ( 130; 131 ) of the acquired digital content data are stored on first storage means ( 203 ), thereby allowing for fast access to said digital content data. The disclosure moreover relates to a device for carrying out such a method. The content sources can be DVD, CD, CD-ROM, hard disk, RAM, Flash memory or remote sources accessible over a network, such as the Internet.

This invention relates to a method of caching a part of digital contentdata retrieved from a content source and a corresponding device forcarrying out such a method.

The development within the area of consumer electronic applications hasbeen tremendous in recent years. Users have got accustomed to advanced,digital devices, which store, acquire, process and/or present data witha huge variety of purposes and functions, such as for example personalcomputers, PDA's, CD-players (portable and non-portable), DVD-players,MP3-players.

This development in the consumer electronic (CE) applications has gonehand in hand with the increasing amounts of data to be stored, acquired,processed and/or presented. For this reason the memory capacities andthe storage, acquisition and processing time have become importantfactors in the popularity of and demand for specific consumer electronicapplications.

Typically, data to be processed by a CE application are stored onvolatile or non-volatile storage means, e.g. a DVD, CD, hard disk,RAM-memory, Flash-memory, and are accessed in a reading operation, wherethe acquisition of data can be in data streams of different size independence on the application and the specific storage means.Alternatively, the data to be processed by a CE application can bestored on a remote data source and can be accessed via a network, e.g.the Internet.

In the field of audio and/or video CE applications an audio and/or video(A/V) stream of data can be presented in a normal playback mode or in aso-called audible and/or visible trick play mode, e.g. audible and/orvisible rewind (REW), fast forward (FFWD) and/or title scan/intro scan,wherein short parts of the A/V data content is presented interleaved bythe A/V CE application. The response times for A/V CE applicationsduring audible and/or visible trick play mode is one out of a pluralityof competitive factors relating to the users' favours, since waiting forthe application to react can be quite a source of irritation.

In general, the trick play mode is typically provided for in one out oftwo ways: by storing at least a part of the content stream in a cachememory from which interleaved content is presented, or by re-acquisitionof the content stream from the content source. The former solution ismemory consuming and the latter is time consuming.

In multimedia CE applications containing disc systems (e.g. hard disks,optical disks), a reading head will typically be acquiring content fromthe disk during normal play back. During trick play by means ofre-acquisition the reading head will be moving rapidly in acquiring datafrom the disk to present segments of the content stream interleaved.This has the problem of causing tear and wear on the system, since itimplies an additional acquisition of data with a rapid movement of thereading head as compared to normal play back.

The other possibility by storing the content in a cache memory duringacquisition so that this cache memory can be sought during trick playprovides for trick play without reacquisition and possibly withoutmovement of the reading head. A drawback with this solution is, asmentioned above, that it is considerably memory consuming, since extramemory is needed to store a complete part of the content stream.

Normally, the two solutions are combined so that a part of the contentstream is kept in a cache memory and so that additional content can beacquired from the content source in case of the trick play continuingbeyond the data kept in the cache memory. Even though this combinationcan make up for some of the disadvantages of the two solutions inthemselves, it is in general not sufficient to provide for an efficienttrick play arrangement with a short response time and reasonable memoryconsumption, where the response time is meant to cover the time fromwhen a user activates a trick play function on an interface on the audioand/or video application device, until the presentation of the requiredtrick play data to the user commences.

An object of the present invention is to provide a method of caching apart of a digital content stream with a time and/or memory efficienttrick play arrangement and a device for performing such a method.

The method according to the invention comprises the step of acquiringthe digital content from a content source, and wherein said part of thedigital content data comprises interleaved segments of the acquireddigital content data, and where the interleaved segments of the acquireddigital content data are stored on first storage means, thereby allowingfor fast access to said part of the digital content data. In this way aninterleaving of cache segments takes place before caching rather than atpresentation, which results in less memory requirements to trick play inan content presentation system and faster trick play response timescompared to prior art content presentation systems.

According to a preferred embodiment of the method, the digital contentdata are digital audio and/or video data Hereby, the method is suitablefor interleaved caching of audio and/or video data from content sources,such as compact discs (CD), CD-ROMs, hard disks (HDD), digital versatilediscs (DVD), random access memory (RAM), Flash memory, or a remotesource, such as Internet radio.

A preferred embodiment of the method according to the invention furthercomprises playing back the stored digital content data stored on thecontent source, and storing of interleaved cache segments takes place ator after replay. Hereby the provision of cache segments for trick playis performed simultaneously with provision of data for play back andwith no further acquisition of the data.

When the storing of interleaved cache segments in the method accordingto the invention depends on parameters, which at least take account forthe probability of replay and/or the acquisition time, an optimisedmethod is provided with the potential that a transition from acquiringdata from the first storage means to reacquiring data from the contentsource means can be performed smoothly, i.e. without breaks in theacquisition.

In a preferred embodiment of the method according to the invention thedigital data are video data in MPEG format and that the interleaved dataare I-pictures, whereby an effective way of choosing the digital contentto be cached interleaved is provided. In yet another preferredembodiment of the method according to the invention the interleaved dataare a continuously acquired part of the digital content data on thedigital content source, whereby short fragments of the digital data atnormal speed are cached interleaved.

In yet another preferred embodiment of the method according to theinvention, the method further comprises storing a first part of thecontent data in a second storage means, which first part of digital datais suitable for use as anti-shock buffer data, where the storing of thedigital data can be continuous or intermittent. Hereby, the method bothprovides for trick play with fast response times and anti-shockbuffering. A continuous storing of the digital content data typically isperformed by acquiring the data at a constant acquisition speed, whereasan intermittent storing of the digital content data can be byacquisition at a fast speed succeeded by a pausing before a nextacquisition at the fast speed.

When the first storage means and the second storage means are comprisedin a single memory circuit as in a preferred embodiment of theinvention, an especially memory efficient method is provided.

In a preferred embodiment of the method, the content source is a storagemedium. Examples of a storage medium are: compact discs (CD), CD-ROMS,hard disks (HDD), digital versatile discs (DVD), random access memory(RAM), Flash memory, etc.

In another preferred embodiment of the method, the content source is aremote source, and the acquisition of the digital content data comprisesreceiving the digital content data over a network. Hereby, the methodcan be used for acquisition of data from a remote source, such asInternet radio.

The invention will be explained more fully below in connection withpreferred embodiments and with reference to the drawing, in which:

FIG. 1 a is a schematic view of a part of data from a content source tobe stored on a storage means according to the prior art;

FIG. 1 b is a schematic view of another part of data from a contentsource to be stored on a storage means according to the prior art;

FIG. 2 shows a schematic view of a part of data from a content source tobe stored on a first storage means according to the invention;

FIG. 3 shows a schematic view of data from a content source to be storedin a first second storage means and in a second storage means accordingto another embodiment of the invention; and

FIG. 4 shows a schematic view of a device for embodying the invention

It should be noted, that the same reference signs are meant to identifythe same features throughout the description of the figures.

FIG. 1 a is a schematic view of a part of data 10 from a content sourceto be stored on a first storage means according to the prior art forplayback and buffering of the data. The horizontal axis shows timeelapsed, and the vertical axis represents digital data. The portion ofdata to the left of the vertical axis represents a rewind buffer, andthe portion of data to the right of the vertical axis represents aforward buffer. The purpose of the forward buffer is both to have ashock buffer (preferably in portable devices) and to provide thepossibility of fast-forward. The data in the rewind buffer is kept toprovide the possibility of fast rewind. Typically, the forward bufferand the rewind buffer are a single buffer memory.

The playback position PLBCK POS is the position of which data is to berepresented as opposed to the acquisition position ACQ. POS. Theacquisition position represents the reading of data stored on the firstdata into buffer. In the figures, the data are shown schematically andthe blocks of data shown are meant to represent shorter or longer partsof data, that can be played back continuously. The interval betweenPLBCK. POS and ACQ. POS represents the size of the forward buffer;typically this Can be up to several minutes of digital audio and/orvideo data for present portable devices.

The figure indicates, that the data 10 contains buffer data 20 and adifferent part of data 30; however, it should be noted that according tothe prior art this data are stored on one and the same storage means,and that the discrimination between the two types of data 20, 30 onlyserves explanatory purposes. According to the prior art, the data 10 areused as an anti-shock buffer in e.g. portable devices, such as portableCD-players, DVD-players, MP3-players, and PDA's. At trick play, the data10 are searched and interleaved segments 30 (shown with horizontalhatching) are played back, i.e. the process of choosing which parts ofdata to present during the trick play is performed after the storage ofthe data 10.

FIG. 1 b is a schematic view of another part of data from a contentsource to be stored on a storage means according to the prior art. InFIG. 1 b data 11, comprising parts of data 21 and 31, are kept in aforward buffer, which serves as a anti-shock buffer (preferably inportable devices); after playback of the data 11 in the buffer, thesedata 11 are thrown away. The forward buffer also provides thepossibility of fast-forward without re-acquisition, where the choice ofwhich parts 31 to present during trick play takes place at presentation.Again, the discrimination between the two types of data 21, 31 onlyserves explanatory purposes and the data 21, 31 are stored on one andthe same storage means. In FIG. 1 b there are no data in a rewind bufferfor fast rewind, so that this function has to entail re-acquisition ofdata from the content source, which is power consuming, can causemechanical wear and tear and which possibly will entail increasedresponse time.

FIG. 2 shows a schematic view of a part of data from a content source tobe stored on a first storage means according to the invention. The firststorage means could be RAM, Flash Memory or a hard disk, whereas thecontent source could be a storage medium, such as a compact disc (CD), aCD-ROM, a hard disk ADD), digital versatile disc (DVD), random accessmemory (RAM), Flash memory, or a remote source such as a network. InFIG. 2, data 110 of digital content are acquired as interleaved segmentsof data 130 from the content source. Naturally, these interleavedsegments are typically stored contiguously in the first storage meansand they are shown here as distinct segments to stress that only afraction of the data from the content source are acquired and stored onthe first storage means for trick lay.

In the case where the digital data are video data in MPEG format, theinterleaved data could be the I-pictures. In other cases the interleaveddata would typically be continuously acquired part of the digitalcontent data on the content source, i.e. short fragments of the digitaldata at normal play back speed.

In FIG. 2 ACQ. POS is shown to the right of PLBCK. POS, which indicates,that acquisition is taking place before playing back. However, in caseof playing back of multiple tracks, e.g. pieces of music from a CD, inan arbitrary order, a cache can be built up in the first storage meansfor this set of tracks, as they are being acquired and played back.These data can be kept or thrown away based on replay probability, whichcan be simulated by means of models (which are beyond the scope of thisinvention), and thus forward cache may exist to the right of ACQ. POSdepending on playback history.

The advantages of this way of caching data from the content source arefaster response time to user requests, no or less re-acquisition in caseof FFWD/REW/Title scan/Intro scan functions and less memory bufferrequirements for buffering for audible and/or visible trick play.

FIG. 3 shows a schematic view of data from a content source to be storedin a first storage means and in a second storage means according toanother embodiment of the invention. Both the first and the secondstorage means could be RAM, flash Memory or a hard disk, whereas thecontent source could be a storage means such as any of the following: acompact disc (CD), a CD-ROM, a hard disk (HDD), digital versatile disc(DVD), random access memory (RAM), or a remote content source such as anetwork.

In FIG. 3, digital content data 111 are acquired as a part of the datafrom the content source, which data 111 are both acquired as interleavedsegments 131 of data and a contiguous part 121 of data. The interleavedsegments 131 are stored contiguously in the first storage means and theyare shown here as distinct segments to stress that only a fraction ofthe data from the content source are acquired and stored as interleavedsegments on the first storage means for use in trick play. Thecontiguous part 121 of the digital data from the content source isstored in the second storage means and serves as an anti-shock buffer.

This storing of both interleaved segments 131 of data for trick play andof a contiguous part 121 of data gives the advantage of having both anintelligent, fast trick play function and an anti-shock buffer, yieldingless mechanical wear and tear, shorter response times, anti-shockbuffering, less power consumption and possibly also less memoryrequirements, depending on the parameters determining the amounts ofdata, which are stored in the first and the second storage means. Theparameters determining the amounts of data for storage could beacquisition time on the content source, i.e. access time, probability ofplay back, the playing position, etc. For instance, the cache size ofone segment 131 of the interleaved stream can be optimised such thatre-acquisition can take place during playback of that particularsegment, in case a user chooses to stop trick play and recommenceplayback at the given position.

In a particular embodiment of the invention, the first and the secondstorage means are comprised in a single memory circuit, whereby noredundant data storage is necessary rendering this embodimentparticularly memory saving.

FIGS. 2 and 3 have been described in relation to content source could bea remote source such as a network or a storage means such as a compactdisc (CD), a CD-ROM, a hard disk ADD), digital versatile disc (DVD),random access memory (RAM) and first and eventually second storage meansbeing a CD, RAM, Flash Memory or a hard disk. Devices for implementingthe method illustrated in FIGS. 2 and 3 could be personal computers,PDA's, CD-players, DVD-players, MP3-players, internet audio players,etc.

It should be noted that interleaved segments 131 to the right of the ACQPOS in FIG. 3 could be present, if a user of the device incorporatingthe method according to the invention has played back some of thedigital content data retrieved from the content source earlier, e.g. atplaying back tracks from a CD in arbitrary order. The abovementionedparameters determining the amounts of data to be stored could includefor how long data should be kept and which data should be kept or thrownaway based on replay probability.

FIG. 4 shows a schematic view of a device for embodying the invention.Shown in FIG. 4 is a device 200 according to the present inventioncomprising one or more microprocessors 201 with a connection to a meansfor receiving 207 a content source and connected to a first storagemeans 203 and a second storage means 204. Shown is also a content source202 to be received in the receiving means 207 in the device 200. Thecontent source 202 is typically a storage medium such a compact disc(CD), a CD-ROM, a hard disk (HDD), digital versatile disc (DVD), randomaccess memory (RAM), and as such the content source could be eitherfixed in the receiving means 207 of the device 200 or be able to beeasily inserted into and retracted from the device 200. However, thecontent source could also be a remote source; in this case the receivingmeans 207 would be means for receiving digital data via a network, e.g.the Internet.

The device 200 could be any digital apparatus comprising a multimediaplayer, e.g. personal computers, CD-players, DVD-players, MP3-players,or PDA's. If the content source is a remote source, the device 200should also contain means for connection to a network, such as a modem,ISDN, ADSL, etc. Such devices are known per se, and therefore only thosefeatures of the device, which are essential for explaining theinvention, will be described. The first and the second storage meanscould be RAM, Flash Memory or a hard disk, and is typically essentiallystationary in the device. In one preferred embodiment of the deviceaccording to the invention, the first and the second storage means arecomprised in a single memory circuit, which is indicated by the brokenline 205. Moreover, the device 200 is provided with a user interface UI206 providing the possibility to navigate through the functions of thedevice. Examples of these functions are: play back, stop, pause,fast-forward (possibly audible and/or visible), rewind (possibly audibleand/or visible), audible and/or visible title scan or intro scan, etc.The user interface typically comprises further components, which liebeyond the scope of this invention and which therefore are not describedhere or shown in the figures. The device 200 further contains components208 for presenting content, such as audio and/or video components forpresenting digital audio and/or video data to a user. Typically, theaudio components are loudspeakers and the video components couldcomprise a screen, a display, a projection display system, etc.

The invention relates to a method of caching a part of digital contentdata from a content source (202), comprising the step of: acquiring thedigital content data from the content source (202), wherein said part ofthe digital content data comprises interleaved segments (130; 131) ofthe acquired digital content data, and said interleaved segments (130;131) of the acquired digital content data are stored on first storagemeans (203), thereby allowing for fast access to said digital contentdata. The invention moreover relates to a device for carrying out such amethod. The content sources can be DVD, CD, CD-ROM, hard disk, RAM,Flash memory or remote sources accessible over a network, such as theInternet.

1. A method of caching a part of digital content data from a content source (202), comprising the step of: acquiring the digital content data from the content source (202), characterized in that said part of the digital content data comprises interleaved segments (130; 131) of the acquired digital content data, and said interleaved segments (130; 131) of the acquired digital content data are stored in a first memory (203), thereby allowing for fast access to said part of the digital content data.
 2. A method according to claim 1, wherein the digital content data are digital audio and/or video data.
 3. A method according to claim 1, characterized in that the method further comprises playing back the digital content data stored on the content source (202), and that the storing of said interleaved segments (130; 131) takes place at or after replay.
 4. A method according to claim 1, characterized in that the storing of the interleaved segments (130; 131) depends on parameters, which at least take account for a probability of replay and/or an acquisition time.
 5. A method according to claim 1, characterized in that the digital content data are video data in MPEG format and that the interleaved segments of the acquired digital content data are I-pictures.
 6. A method according to claim 1, characterized in that each of the interleaved segments (130; 131) of the acquired digital content data is a continuously acquired part of the digital content data from the content source (202).
 7. A method according to claim 1, characterized in that the method further comprises storing a contiguous first part of the digital content data in a second memory (204), which contiguous part (121) of the digital content data is suitable for use as anti-shock buffer data.
 8. A method according to any of the claim 7, characterized in that the first memory (203) and the second memory (204) are comprised in a single memory circuit (205).
 9. A method according to claim 1, wherein the content source (202) is a storage medium.
 10. A method according to claim 1, wherein the content source (202) is a remote source and wherein the acquisition of the digital content data comprises receiving the digital content data over a network.
 11. A device for caching a part of digital content data from a content source, comprising means for acquiring the digital content data from the content source, characterized in that the device (200) further comprises first memory (203) arranged to store interleaved segments (130; 131) of the acquired digital data, thereby allowing for fast access to said part of digital content data.
 12. A device according to claim 11, wherein the digital content data are digital audio and/or video data.
 13. A device according to claim 11, characterized in that the device further comprises means for playing back (207) the digital content data stored on the first memory (203), and the first memory (203) is adapted to store said interleaved segments (130; 131) at or after replay.
 14. A device according to claim 11, characterized in that the device further comprises decision means (201), which are arranged to, in dependence on parameters taking account for a probability of replay and/or an acquisition time, decide which part of the digital content data is to be stored.
 15. A device according to any of the claim 11, characterized in that the digital content data are video data in MPEG format and that the interleaved segments of the acquired digital content data are I-pictures.
 16. A device according to claim 11, characterized in that each of the interleaved segments (130; 131) of the acquired digital content data is a continuously acquired part of the digital content data from the content source (202).
 17. A device according to claim 11, characterized in that the device (200) further comprises a second memory (204) suitable as an anti-shock buffer, which second memory (204) are adapted for storing of a contiguous part (121) of the digital content data, which contiguous part (121) of the digital content data is suitable for use as anti-shock buffer data.
 18. A device according to claim 17, characterized in that the first memory (203) and the second memory (204) are comprised in a single memory circuit (205).
 19. A device according to claim 11, wherein the content source (202) is a storage medium.
 20. A device according to claim 11, wherein the content source (202) is a remote source, and wherein the means for acquiring the digital content data comprises means for receiving data over a network. 